The primary aims of the study are: 1) to compare the effectiveness of lithium carbonate, imipramine, placebo, and a combination of lithium and imipramine in the long-term maintenance treatment of unipolar recurrent affective illness, and 2) to compare the effectiveness of lithium carbonate, imipramine, and a combination of lithium and imipramine in the long-term maintenance treatment of bipolar recurrent affective illness. The secondary aims of the study are: 1) to identify demographic or clinical variables which are related to treatment outcome; 2) to determine whether the study treatments "prevent" or merely "attenuate" depressive and manic recurrences; and 3) to determine whether affective recurrences can be successfully treated by increasing the dose of maintenance medication. There is particular interest in determining whether increasing the plasma level of lithium in patients who have depressive recurrences has antidepressant value.